FROM "INFANTILE" TO ELDERLY: A RARE CAUSE OF HYPERCALCEMIA NOT TO BE MISSED IN THE GERIATRIC POPULATION

Idiopathic infantile hypercalcemia (IIH) is a rare, parathyroid hormone (PTH)-independent disorder of calcium metabolism. It is most often caused by mutations in the CYP24A1 gene that impair vitamin D catabolism. We report a 70-year-old male with persistent hypercalcemia (Ca 13.2 mg/dL) and low-normal PTH levels. Extensive evaluation excluded malignancy, granulomatous disease, and vitamin D intoxication. Genetic analysis revealed a homozygous CYP24A1 variant (c.233G>T; p.Gly78Val), consistent with CYP24A1 deficiency. Bisphosphonate therapy with zoledronic acid rapidly and sustainably normalized calcium levels for 10 months. The patient's daughter was a heterozygous carrier. This confirmed autosomal-recessive inheritance. This case illustrates an atypical late-onset presentation of CYP24A1 deficiency. It emphasizes the importance of considering this diagnosis in adults with PTH-independent hypercalcemia, especially when seasonal variation and family history are present. Recognition of CYP24A1 deficiency at all ages highlights the need for genotype-based terminology rather than the misleading label "infantile" hypercalcemia.